1. Field of the Invention
The invention relates to a linear motion unit having a runner that is arranged so as to be movable back and forth on a rod along the rod""s axis, and also having at least one lubricating device which at least partially surrounds the rod and which includes at least one lubricating element that stands in lubricating contact with the rod and at least one lubricant reservoir that is immovably joined to the runner.
2. The Prior Art
Such a linear motion unit is known, for example from EP 0,874,172 A1. In this linear motion unit embodied as a roller spindle drive, two lubricating devices are arranged on the axial ends of the runner assembly and axially contiguous thereto. Each lubricating device is composed of a lubricating element of a polymer foam that contains lubricant and that is in lubricating engagement with the threaded spindle. In addition, each lubricating device has a lubricant reservoir that is axially adjacent to the lubricating element and is connected to the lubricating element by a passage, so that more lubricant can be supplied to the lubricating element from the lubricant reservoir in the event of excessive consumption of lubricant.
A major disadvantage of this known linear motion unit is the small active lubricating length of its lubricating elements, which results in a high contact pressure of the lubricating elements and correspondingly severe wear of the polymer foam material. In addition, all dirt wiped from the surface of the rod is deposited in the pores of the polymer foam material, a clogging it. This can impede the dispensing of lubricant and can also lead to hardening of the polymer foam material, both of which impair adequate lubricating contact of the lubricating elements with the surface of the rod.
In addition, linear motion units are known from DE 198 33 228 A1 and U.S. Pat. No. 5,749,266, which disclose lubricating devices comprised of lubricating elements made of polymer foam that contains lubricant. Furthermore, DE 197 54 454 A1 discloses a linear motion unit in which the lubricating device has an external lubricant reservoir. For the sake of completeness, reference is also made to DE 299 19 250 U1 regarding the state of the art.
In contrast to the prior art devices, the object of the invention is to provide a linear motion unit of the aforementioned type which permits the use of lubricating elements with large active lubricating length while preserving compact construction of the overall linear motion unit.
This object is attained in accordance with the invention through a linear motion unit of the class in which the lubricant reservoir is arranged radially outside the lubricating element with respect to the axis of the rod. In comparison with the known lubricating device from the class-defining EP 0,874,172 A1, the lubricating element can thus have a significantly greater extension in the direction of the rod axis with the same axial length of the lubricating device and the same supply volume of the lubricant reservoir, so that the aforementioned disadvantages thereof can be avoided in a simple manner in accordance with the invention. Consequently, in the most favorable case, the entire axial extent of the lubricating device can be used to lubricate the surface of the rod. The lubricating element should advantageously have an active lubricating length of at least 15 mm, preferably at least 25 mm.
The radially concentric arrangement of lubricating element and lubricant reservoir can be provided in a simple manner in the case of a lubricating device having only a lubricating function in that the lubricating device has a base body on whose inner circumferential surface is arranged at least one lubricating element, and whose outer circumferential surface forms, at least in part, an inner boundary wall of the lubricant reservoir. In accordance with the invention, the lubricating device need not fully enclose the rod. Rather, it can still perform its function if it merely extends around the rod in a U-shaped or horseshoe manner. With regard to sealing of the lubricating device toward the outside, it is preferred for purposes of simplifying the constructive design for the base body to be designed in a sleeve shape.
To provide the outer boundary wall of the lubricant reservoir, it is possible in accordance with another embodiment of the invention to provide a preferably sleeve-shaped cover body whose inner circumferential surface encloses the outer circumferential surface of the base body at a distance over at least part of its length. Alternatively, it is also possible for the outer boundary wall of the lubricant reservoir to be formed by the inner circumferential surface of a recess in the runner or a part connected thereto. In the latter case, the receiving volume of the lubricant reservoir can be increased by sectional enlargement of this recess.
Simple and cost-effective manufacture results when the base body and, if applicable, the cover body are manufactured as injection-molded parts, preferably of plastic.
To facilitate the resupply of lubricant from the lubricant reservoir to the lubricating element, it is proposed that at least one radial connecting opening may be provided in the base body through which the lubricant contained in the lubricant reservoir can reach the at least one lubricating element. As is described below in greater detail, the throughput of lubricant can be influenced by the size and shape of the connecting opening and/or by elements arranged in this opening.
A variety of embodiments are also conceivable with respect to the interior design of the base body of the lubricating device.
In one embodiment, the inner circumferential surface of the base body can have at least one helical groove in which a correspondingly helical lubricating element is accommodated. If the linear motion unit is a roller spindle drive and if the threaded spindle of the roller spindle drive has a plurality of spindle grooves, i.e. if the threaded spindle is multiple-threaded, then it is advantageous for the lubricating device to also have a number of helical lubricating elements that corresponds to the number of threads and each of which lubricates one of the spindle grooves. If the intention is to lubricate not just the spindle grooves of the threaded spindle, but also the rest of the outer circumferential surface of the threaded spindle, then additional lubricating elements can be provided on the inner circumferential surface of the base body for this purpose. It is advantageous for each of the thread grooves to be in lubricant exchange contact with the lubricant reservoir via its own connecting opening.
In another embodiment, at least one axially-extending groove in which a lubricating strip is accommodated can be formed in the inner circumferential surface of the base body. Such a lubricating strip can, of course, touch only the outer circumferential surface of the rod and thus wet it with lubricant. However, if the spindle grooves of a rod embodied as a threaded spindle are also to be supplied with lubricant, then the lubricating strip can further possess a plurality of projections, each of which engages a corresponding spindle groove. If lubrication of the remaining outer circumferential surface of the threaded spindle is to be avoided, this can be accomplished by appropriately long wetting of the projections which engage the spindle grooves. By this means, the connecting sections of the lubricating strip located between two adjacent projections can be spaced apart from the outer circumferential surface of the threaded spindle.
It is advantageous for the lubricating element to extend over essentially the entire length of the groove. However, if sufficient axial space is available, a wiping element can be arranged in the groove ahead of and/or behind the lubricating element viewed in the direction of the groove""s extension, such wiping element""s purpose being primarily to wipe from the surface of the rod dirt particles that enter the lubricating region and to keep them away from the actual lubricating element. In addition, the wiping element also serves to wipe excess lubricant from the rod surface and thus to contribute to uniform lubrication of the linear motion unit.
The axial groove embodiment discussed above has the advantage of simpler manufacture, while the helical groove embodiment has the advantage that the helical lubricating element is in lubricating contact with the spindle groove over a greater path length, which both increases lubricating efficiency and reduces loading on the lubricating element.
To be able to facilitate the transport of lubricant from the lubricant reservoir to the lubricating element, it is proposed that at least one groove, preferably running in the circumferential direction, be formed in the outer circumferential surface of the base body, in which groove a lubricant intake element is accommodated. Lubricant exchange between this intake element and the lubricating element can be ensured in a variety of ways. For example, the lubricant intake element can have at least one radially internal projection that engages a corresponding connecting opening and is in lubricant exchange contact with a corresponding lubricating element, i.e. in particular touches the corresponding lubricating element. It is also possible to place a specially manufactured wick element, which assumes the function of this projection, in the connecting opening.
Polymer foam, in particular open-cell polymer foam, has proven its utility as a material for the at least one lubricating element and/or the at least one lubricant intake element and/or the at least one wick element. Preferably, the at least one lubricating element and/or the at least one lubricant intake element and/or the at least one wick element can be cut from a polymer foam sheet material, for example by water jet cutting. This also applies for helical lubricating elements which are cut in the shape of a spiral, for example, where the value of the radius of the innermost turn of this spiral corresponds to at least the value of the desired helix radius of the helical lubricating element. The spiral thus obtained can then be pulled or formed into a helix, taking advantage of the flexibility of the foam plastic or polymer foam material, and can be placed in the helical groove in the inner surface of the base body of the lubricating device.
It is also conceivable that the at least one wick element is embodied as a membrane, preferably as a one-way membrane opening from the lubricant reservoir toward the lubricating element.
In a refinement of the invention, it is possible to provide on at least one, and preferably both, of the axial longitudinal ends of the lubricating device a sealing device that prevents the undesirable escape of lubricant from the lubricating device. Preferably, this sealing device is identical in construction to the seals that are provided at the axially longitudinal ends of the threaded nut unit.
Because of the design of the lubricating device with a lubricant reservoir, the linear motion unit explained above is provided with adequate lubrication for a long period of time, if not its entire lifetime. To be able to ensure adequate lubrication over the entire lifetime of the linear motion unit even under high loading, and thus high lubricant consumption, provision can be made for the lubricant reservoir to have a connection for lubricant filling. The lubricant can be lubricating grease or, preferably, lubricating oil.
It must also be mentioned that the runner, which is known per se, or a mounting unit fastened thereto can be used to attach a functional unit that is to be moved by the linear motion unit. Moreover, it has proven advantageous for the lubricating device to be arranged essentially completely within the axial extent of the runner and/or the mounting unit.
Particularly when the linear motion unit is designed as a roller spindle drive, the load exerted on the mounting unit need not be transmitted through the threaded nut unit to the threaded spindle at all or at least only to a negligible extent. Rather, this load can be transmitted to an extruded rail which is supported in a load-bearing manner on a guide housing. Since the threaded nut unit thus need only perform the function of transforming a rotary motion of the threaded spindle into a linear motion of the runner, it can be relatively short in the axial direction, in particular significantly shorter than the mounting unit whose length is determined solely by the requirement to provide a large variety of mounting options for the functional units that can be moved by the linear motion unit. Thus, space for accommodating the lubricating devices can easily be created in the runner and/or the mounting unit, or existing and previously unused space can be used to accommodate the lubricating devices. It can easily be seen that the runner and the mounting unit would thus have a shorter overall length in the axial direction and that this shorter overall length can be used directly to increase the travel distance of the roller spindle drive without further changes to the roller spindle drive.
According to the invention, the entire axial extent of the lubricating device need not be accommodated within the axial extent of the runner and/or the mounting unit. Rather, when the basic idea of the present invention is utilized, a considerable reduction in the length of the runner can be achieved when at least 70%, and preferably at least 90%, of the axial extent of the lubricating device is arranged within the axial extent of the runner and/or of the mounting unit.
As a further feature of the invention, the concept of arranging the lubricating device essentially within the axial extent of the runner and/or the mounting unit can also be used independently of the radially contiguous arrangement of lubricating element and lubricant reservoir. Consequently, independent protection is being sought for this concept.
The invention explained above can be used to advantage in such applications as a roller spindle drive, especially a ball screw, which comprises a threaded spindle-forming the rod-with a spindle axis, wherein at least one spindle groove is provided in the outer circumferential surface of the threaded spindle, and also comprises a threaded nut unit which forms at least part of the runner and surrounds the threaded spindle, with at least one spindle return groove which, together with the associated spindle groove of the threaded spindle, forms a thread channel, wherein the thread channel is part of a closed circulating channel which accommodates a continuous series of rollers.
To ensure a relative position of the lubricating device and threaded spindle which guarantees the desired thread engagement of the spindle groove(s) and lubricating groove(s), at least one alignment pin may be placed in the base body, preferably screwed into it, that engages a spindle groove of the threaded spindle. In principle, the engagement of this alignment pin with the spindle groove is only necessary during assembly of the roller spindle drive, since later in operation the correct alignment is maintained by the attachment of the individual assemblies to one another. So as not to unnecessarily hinder operation of the roller spindle drive, the alignment pin can thus be removed again, or at least withdrawn somewhat, after assembly is completed. It is also possible to manufacture at least the head portion of the alignment pin which engages the spindle groove of a material that wears quickly in operation, for example a soft plastic.